The present invention relates to a semiconductor device and a forming method. More specifically, the present invention relates to a technology that is applicable, for instance, to a resistance random access memory (ReRAM).
The ReRAM is currently developed as a nonvolatile memory. The ReRAM is a memory that uses a variable resistance element. In an initial state, the variable resistance element is an insulator. As described, for instance, in Japanese Unexamined Patent Application Publication No. 2010-218615, the variable resistance element decreases its resistance when subjected to forming. In forming, a high voltage (forming voltage) is applied to the variable resistance element. After forming, the variable resistance element is in either a high-resistance state or a low-resistance state. When a voltage is applied to the variable resistance element, the variable resistance element can switch from the high-resistance state to the low-resistance state or from the low-resistance state to the high-resistance state. The ReRAM retains either “0” or “1” as data depending on whether the variable resistance element is in the high-resistance state or the low-resistance state.
An example of the ReRAM is described in Japanese Unexamined Patent Application Publication No. 2005-25914. This ReRAM includes a plurality of memory cells, a plurality of plate lines, and a plurality of bit lines. Each memory cell includes a transistor and a variable resistance element. The drain of the transistor is coupled to a plate line through the variable resistance element. The source of the transistor is coupled to a bit line. A voltage between the plate line and the bit line causes the variable resistance element in each memory cell to switch from the high-resistance state to the low-resistance state or from the low-resistance state to the high-resistance state.